An RFID Expert: What is passive RFID?

The abbreviation RFID stands for “Radio Frequency Identification”. RFID is a contactless identification technology that has been developed for storing and retrieving data at a distance using a transmitter/receiver system (reader) and markers (tags). This technology is based on the emission of electromagnetic fields received by an antenna matched with an electronic chip, allowing automatic identification of various objects, vehicles and people.

RFID tags

RFID tags are small objects such as rugged or flexible tags, adhesive labels, disc tags, badges, key fobs… containing an integrated circuit and an antenna for receiving and responding to radio signals transmitted by the transmitter/receiver (reader). The circuits contain an identifier and may also host other data.

RFID readers

Readers are active items of equipment emitting radiofrequency signals that activate any tags entering their field by providing the energy required by the tag.

RFID frequencies

Several communications frequencies can be used by RFID technology:

Low frequency: 125 kHz

High frequency: 13.56 MHz

Ultra-high frequency: 433 MHz, 863 to 915 MHz, 2.45 GHz

How does it work?

When the tags (transponders) are "woken" by the reader, a predefined communication protocol is used for data exchange between the items. Unlike barcodes, RFID does not require the reader to be brought close to the product to enable the identification process. Tags can be read in a range of a few centimeters to several tens of meters in some cases, and can be beyond the line of sight of the reader. Depending on the model used, tags may have read-only functionality or allow additional information to be written to them.

In order to communicate, the tag and reader need to be on the same frequency, but like a radio set, the frequencies can be on a wide spectrum from low to very high frequencies. RFID tags are formed by the pairing of an integrated circuit (chip) and an antenna and are affixed on a product or container.

The antenna is tuned to a specific frequency, and captures the electromagnetic signal sent by the reader. Some tags are referred to as "passive". In this case, the signal has to have a certain power and uses induction to generate a current in the chip. "Active" or "semi-active" tags come with a battery to power the chip. The signal required with such chips can be lower-power and can be received over a greater distance. This signal simply activates the tag.

Once the activation signal is received, the chip transmits the information it contains. Some tags also have a memory system enabling data to be written to them.